Optimizing tunnel monitoring in sdn

ABSTRACT

A method implemented by a first switch in a software defined networking (SDN) network to monitor a tunnel between the first switch and a second switch in the SDN network. The method includes generating a first flow entry that matches packets received over the tunnel, generating a second flow entry that matches packet received over the tunnel, where the second flow entry has a priority that is lower than a priority of the first flow entry, removing the first flow entry and transmitting a flow removed message to an SDN controller in response to a determination that the first flow entry has timed out, maintaining a statistic associated with the second flow entry, and transmitting a statistics trigger event message to the SDN controller in response to a determination that the statistic associated with the second flow entry exceeds a threshold value.

TECHNICAL FIELD

Embodiments of the invention relate to the field of computer networks,and more specifically, to optimizing tunnel monitoring in softwaredefined networking (SDN) networks.

BACKGROUND

Software defined networking (SDN) is an approach to computer networkingthat employs a split architecture network in which the forwarding plane(sometimes referred to as the data plane) is decoupled from the controlplane. The use of a split architecture network simplifies the networkdevices (e.g., switches) implementing the forwarding plane by shiftingthe intelligence of the network into one or more controllers thatoversee the switches. SDN facilitates rapid and open innovation at thenetwork layer by providing a programmable network infrastructure.

OpenFlow is a protocol that enables controllers and switches in an SDNnetwork to communicate with each other. OpenFlow enables dynamicprogramming of flow control policies in the network. An OpenFlow switchincludes a programmable packet processing pipeline (sometimes referredto as the OpenFlow pipeline). The OpenFlow pipeline includes one or moreflow tables, where each flow table includes one or more flow entries.The flow tables of an OpenFlow pipeline are sequentially numbered,starting from zero. Pipeline processing starts at the first flow table(e.g., flow table 0). When processed by a flow table, a packet ismatched against the flow entries of the flow table to select a flowentry. If a flow entry is found, the instruction set included in thatflow entry is executed.

The forwarding plane in an SDN network typically includes one or moreswitches that are connected to each other via a full mesh of tunnels.The tunnels are typically implemented using technologies such as VirtualeXtensible Local Area Network (VxLAN), Generic Routing Encapsulation(GRE), Multiprotocol Label Switching (MPLS), or similar tunnelingtechnology. To create a full mesh of tunnels for a group of n switches,(n*(n−1))/2 tunnels are needed. Each switch will have (n−1) tunnel endpoints, one for each tunnel towards the other switches. Serviceconnectivity applications such as Service Chain Function (SCF), EthernetLocal Area Network (e-LAN), and Layer 3 Virtual Private Network (L3VPN)can utilize these tunnels to send traffic.

The tunnels in the SDN network need to be monitored in order to avoidprolonged service disruptions. One conventional technique to monitor atunnel is for the SDN controller to generate a special packet and insertthe special packet into one end point of the tunnel. Once the specialpacket reaches the other end point of the tunnel, the special packet canbe encapsulated and sent to the SDN controller. The SDN controller cancompare the number of special packets that were sent with the number ofspecial packets that were received to determine the health of thetunnel. If the health of the tunnel is deemed to be poor, the SDNcontroller can take appropriate actions to restore the health of thetunnel.

Another conventional technique to monitor a tunnel is for the switchesto run protocols such as Bi-directional Forwarding Detection (BFD) andLink Layer Discovery Protocol (LLDP), and rely on the protocol statemachine to detect failures. With BFD, the switches periodically exchangeBFD keep-alive packets with each other. As long as a switch receives akeep-alive packet from its peer switch, the switch assumes that thetunnel between the switches is operational. If a switch fails to receivea certain number of keep-alive packets from its peer switch within aspecific period of time (e.g., at least 3 keep-alive packets within 10milliseconds), then the switch assumes that the tunnel between theswitches has failed, and may take corrective action.

The conventional tunnel monitoring techniques described above rely oninjecting explicit tunnel monitoring packets into a tunnel. For example,BFD periodically sends bidirectional keep-alive packets over a tunnel.These bidirectional keep-alive packets are sent even when the tunnel iscarrying normal data traffic. As such, these keep-alive packetsunnecessarily consume tunnel bandwidth. For example, for a BFD sessionwith a keep-alive interval of 3 milliseconds, around 333 keep-alivepackets are sent per second, where the size of each keep-alive packetranges from around 80 to 110 bytes. Thus, around 66 kilobytes per secondof the tunnel bandwidth is used for tunnel monitoring purposes. Also,processing the keep-alive packets and updating the protocol statemachine consumes valuable processing resources at the switches, whichcan result in reduced packet processing speed and even packet loss.

SUMMARY

A method is implemented by a first switch in a software definednetworking (SDN) network to monitor a tunnel between the first switchand a second switch in the SDN network. The method includes generating afirst flow entry that matches packets received over the tunnel,generating a second flow entry that matches packet received over thetunnel, where the second flow entry has a priority that is lower than apriority of the first flow entry, removing the first flow entry andtransmitting a flow removed message to an SDN controller in response toa determination that the first flow entry has timed out, maintaining astatistic associated with the second flow entry, and transmitting astatistics trigger event message to the SDN controller in response to adetermination that the statistic associated with the second flow entryexceeds a threshold value.

A network device is configured to function as a first switch in asoftware defined networking (SDN) network to monitor a tunnel betweenthe first switch and a second switch in the SDN network. The networkdevice includes a set of one or more processors and a non-transitorymachine-readable storage medium having stored therein a tunnelmonitoring component. The tunnel monitoring component, when executed bythe set of one or more processors, causes the network device to generatea first flow entry that matches packets received over the tunnel,generate a second flow entry that matches packet received over thetunnel, wherein the second flow entry has a priority that is lower thana priority of the first flow entry, remove the first flow entry andtransmit a flow removed message to an SDN controller in response to adetermination that the first flow entry has timed out, maintain astatistic associated with the second flow entry, and transmit astatistics trigger event message to the SDN controller in response to adetermination that the statistic associated with the second flow entryexceeds a threshold value.

A non-transitory machine-readable medium has computer code storedtherein, which when executed by a set of one or more processors of anetwork device functioning as a first switch in a software definednetworking (SDN) network, causes the network device to performoperations for monitoring a tunnel between the first switch and a secondswitch in the SDN network. The operations include generating a firstflow entry that matches packets received over the tunnel, generating asecond flow entry that matches packet received over the tunnel, wherethe second flow entry has a priority that is lower than a priority ofthe first flow entry, removing the first flow entry and transmitting aflow removed message to an SDN controller in response to a determinationthat the first flow entry has timed out, maintaining a statisticassociated with the second flow entry, and transmitting a statisticstrigger event message to the SDN controller in response to adetermination that the statistic associated with the second flow entryexceeds a threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. In the drawings:

FIG. 1 is a block diagram of an SDN network in which tunnel monitoringcan be implemented, according to some embodiments.

FIG. 2 is a diagram illustrating operations by an SDN controller toconfigure a tunnel between two switches, according to some embodiments.

FIG. 3 is a diagram illustrating operations by a switch and an SDNcontroller when a failure detect flow entry times out, according to someembodiments.

FIG. 4 is a diagram illustrating operations by a switch and an SDNcontroller when a statistic associated with a recovery detect flow entryexceeds a threshold value, according to some embodiments.

FIG. 5 is a flow diagram of a process for monitoring a tunnel in an SDNnetwork, according to some embodiments.

FIG. 6 is a flow diagram of a process for monitoring a tunnel in an SDNnetwork, according to some embodiments.

FIG. 7A illustrates connectivity between network devices (NDs) within anexemplary network, as well as three exemplary implementations of theNDs, according to some embodiments.

FIG. 7B illustrates an exemplary way to implement a special-purposenetwork device according to some embodiments.

FIG. 7C illustrates various exemplary ways in which virtual networkelements (VNEs) may be coupled according to some embodiments.

FIG. 7D illustrates a network with a single network element (NE) on eachof the NDs, and within this straight forward approach contrasts atraditional distributed approach (commonly used by traditional routers)with a centralized approach for maintaining reachability and forwardinginformation (also called network control), according to someembodiments.

FIG. 7E illustrates the simple case of where each of the NDs implementsa single NE, but a centralized control plane has abstracted multiple ofthe NEs in different NDs into (to represent) a single NE in one of thevirtual network(s), according to some embodiments.

FIG. 7F illustrates a case where multiple VNEs are implemented ondifferent NDs and are coupled to each other, and where a centralizedcontrol plane has abstracted these multiple VNEs such that they appearas a single VNE within one of the virtual networks, according to someembodiments.

FIG. 8 illustrates a general purpose control plane device withcentralized control plane (CCP) software 850), according to someembodiments.

DETAILED DESCRIPTION

The following description describes methods and apparatus for monitoringa tunnel in a software defined networking (SDN) network. In thefollowing description, numerous specific details such as logicimplementations, opcodes, means to specify operands, resourcepartitioning/sharing/duplication implementations, types andinterrelationships of system components, and logicpartitioning/integration choices are set forth in order to provide amore thorough understanding of the present invention. It will beappreciated, however, by one skilled in the art that the invention maybe practiced without such specific details. In other instances, controlstructures, gate level circuits and full software instruction sequenceshave not been shown in detail in order not to obscure the invention.Those of ordinary skill in the art, with the included descriptions, willbe able to implement appropriate functionality without undueexperimentation.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

Bracketed text and blocks with dashed borders (e.g., large dashes, smalldashes, dot-dash, and dots) may be used herein to illustrate optionaloperations that add additional features to embodiments of the invention.However, such notation should not be taken to mean that these are theonly options or optional operations, and/or that blocks with solidborders are not optional in certain embodiments of the invention.

In the following description and claims, the terms “coupled” and“connected,” along with their derivatives, may be used. It should beunderstood that these terms are not intended as synonyms for each other.“Coupled” is used to indicate that two or more elements, which may ormay not be in direct physical or electrical contact with each other,co-operate or interact with each other. “Connected” is used to indicatethe establishment of communication between two or more elements that arecoupled with each other.

An electronic device stores and transmits (internally and/or with otherelectronic devices over a network) code (which is composed of softwareinstructions and which is sometimes referred to as computer program codeor a computer program) and/or data using machine-readable media (alsocalled computer-readable media), such as machine-readable storage media(e.g., magnetic disks, optical disks, solid state drives, read onlymemory (ROM), flash memory devices, phase change memory) andmachine-readable transmission media (also called a carrier) (e.g.,electrical, optical, radio, acoustical or other form of propagatedsignals—such as carrier waves, infrared signals). Thus, an electronicdevice (e.g., a computer) includes hardware and software, such as a setof one or more processors (e.g., wherein a processor is amicroprocessor, controller, microcontroller, central processing unit,digital signal processor, application specific integrated circuit, fieldprogrammable gate array, other electronic circuitry, a combination ofone or more of the preceding) coupled to one or more machine-readablestorage media to store code for execution on the set of processorsand/or to store data. For instance, an electronic device may includenon-volatile memory containing the code since the non-volatile memorycan persist code/data even when the electronic device is turned off(when power is removed), and while the electronic device is turned onthat part of the code that is to be executed by the processor(s) of thatelectronic device is typically copied from the slower non-volatilememory into volatile memory (e.g., dynamic random access memory (DRAM),static random access memory (SRAM)) of that electronic device. Typicalelectronic devices also include a set or one or more physical networkinterface(s) (NI(s)) to establish network connections (to transmitand/or receive code and/or data using propagating signals) with otherelectronic devices. For example, the set of physical NIs (or the set ofphysical NI(s) in combination with the set of processors executing code)may perform any formatting, coding, or translating to allow theelectronic device to send and receive data whether over a wired and/or awireless connection. In some embodiments, a physical NI may compriseradio circuitry capable of receiving data from other electronic devicesover a wireless connection and/or sending data out to other devices viaa wireless connection. This radio circuitry may include transmitter(s),receiver(s), and/or transceiver(s) suitable for radiofrequencycommunication. The radio circuitry may convert digital data into a radiosignal having the appropriate parameters (e.g., frequency, timing,channel, bandwidth, etc.). The radio signal may then be transmitted viaantennas to the appropriate recipient(s). In some embodiments, the setof physical NI(s) may comprise network interface controller(s) (NICs),also known as a network interface card, network adapter, or local areanetwork (LAN) adapter. The NIC(s) may facilitate in connecting theelectronic device to other electronic devices allowing them tocommunicate via wire through plugging in a cable to a physical portconnected to a NIC. One or more parts of an embodiment of the inventionmay be implemented using different combinations of software, firmware,and/or hardware.

A network device (ND) is an electronic device that communicativelyinterconnects other electronic devices on the network (e.g., othernetwork devices, end-user devices). Some network devices are “multipleservices network devices” that provide support for multiple networkingfunctions (e.g., routing, bridging, switching, Layer 2 aggregation,session border control, Quality of Service, and/or subscribermanagement), and/or provide support for multiple application services(e.g., data, voice, and video).

FIG. 1 is a block diagram of an SDN network in which tunnel monitoringcan be implemented, according to some embodiments. The SDN network 100includes an SDN controller 110 that is communicatively coupled toswitches 120 (e.g., switches 120A-C). In one embodiment, the SDNcontroller 110 and the switches 120 communicate using a southboundcommunications protocol such as OpenFlow (e.g., OpenFlow 1.5) or similarsouthbound protocol. The SDN controller 110 may use OpenFlow or asimilar southbound protocol to configure and manage the forwardingbehavior of the switches 120. For clarity and ease of understanding,embodiments are primarily described in a context where OpenFlow is usedas the southbound communication protocol between the SDN controller 110and the switches 120. However, it should be understood that the SDNcontroller 110 and the switches 120 can communicate using other types ofsouthbound communication protocols and that the tunnel monitoringtechniques disclosed herein can be implemented in a context where theSDN controller 110 and the switches 120 use other types of southboundcommunications protocols without departing from the spirit and scope ofthe present disclosure. For sake of illustration the SDN network 100 isshown as including a single SDN controller 110 that manages threeswitches 120. However, it should be understood that the SDN network 100can include more than one SDN controller 110 and that each SDNcontroller 110 can manage more or less than three switches 120.

Each switch 120 may include a packet processing pipeline that includes aset of flow tables. Each flow table may include a set of flow entries,where each flow entry includes a packet matching criteria (e.g., carriedin a match field) and a corresponding set of instructions to executewhen a packet matches the packet matching criteria. A packet is said tomatch a flow entry if the packet matches the packet matching criteria ofthe flow entry. In one embodiment, when a switch 120 receives a packetin the data plane, the switch 120 initially matches the packet againstflow entries in the foremost flow table of the packet processingpipeline. The switch 120 may then continue to match the packet againstflow entries in subsequent flow tables of the packet processingpipeline. If the packet matches a flow entry, then the switch 120executes the corresponding set of instructions of that flow entry. Inone embodiment, flow entries are assigned a priority. If the packetmatches the packet matching criteria of multiple flow entries within aflow table, only the flow entry having the highest priority is selected(and its instructions to executed). The set of instructions specified ina flow entry may include, for example, instructions to modify thepacket, direct the packet to another flow table in the packet processingpipeline, and/or output the packet to a specified port.

In one embodiment, the switches 120 are connected to each other via afull mesh of tunnels. The tunnels may be implemented using technologiessuch as VxLAN, GRE, MPLS, or similar tunneling technology. To create afull mesh of tunnels for a group of n switches 120, (n*(n−1))/2 tunnelsare needed. Each switch will have (n−1) tunnel end points, one for eachtunnel towards the other switches 120. Service connectivity applicationssuch as Service Chain Function (SCF), Ethernet Local Area Network(e-LAN), and Layer 3 Virtual Private Network (L3VPN) can utilize thesetunnels to send traffic.

The tunnels in the SDN network 100 need to be monitored in order toavoid prolonged service disruptions. Conventional tunnel monitoringtechniques typically rely on injecting explicit tunnel monitoringpackets into a tunnel. As used herein, explicit tunnel monitoring refersto a tunnel monitoring technique where packets are injected into atunnel, where the sole or primary purpose of these packets is to monitorthe tunnel (and not for carrying user data). For example, BFDperiodically sends bidirectional keep-alive messages over a tunnel.These bidirectional keep-alive messages are sent even when the tunnel iscarrying normal data traffic. As such, these keep-alive messagesunnecessarily consume tunnel bandwidth. For example, for a BFD sessionwith a keep-alive interval of 3 milliseconds, around 333 keep-alivemessages are sent per second, where the size of each keep-alive messageranges from around 80 to 110 bytes. Thus, around 66 kilobytes per secondof the tunnel bandwidth is used for tunnel monitoring purposes. Also,processing the keep-alive messages and updating the protocol statemachine consumes valuable processing resources at the switches 120,which can result in reduced packet processing speed and even packetloss.

Embodiments disclosed herein overcome some of the disadvantages of theconventional techniques by using the existing traffic flowing through atunnel to determine whether the tunnel is operational and by onlyresorting to explicit tunnel monitoring techniques (e.g., that injectexplicit tunnel monitoring packets into the tunnel) when there is notraffic flowing through the tunnel for a period of time. This is basedon the observation that when traffic is flowing through the tunnel,there is no need to inject explicit tunnel monitoring packets into thetunnel since it can be inferred from the existing traffic flowingthrough the tunnel that the tunnel is operational. As will be describedin additional detail below, embodiments may achieve this by programminga particular set of flow entries in the switches 120 at the end pointsof the tunnel. As will become apparent from the disclosure providedherein, an advantage of the embodiments disclosed herein is that theyonly resort to explicit tunnel monitoring when there is no trafficflowing through the tunnel, and thus the bandwidth usage of the tunneland the processing load at the end points of the tunnel (e.g., theswitches 120) can be reduced.

FIG. 2 is a diagram illustrating operations by an SDN controller toconfigure a tunnel between two switches, according to some embodiments.As shown in the diagram, SDN controller 110 may program switch 120A andswitch 120B to configure tunnel 210 between switch 120A and switch 120B.In one embodiment, explicit tunnel monitoring is initially disabled fortunnel 210. In one embodiment, SDN controller 110 programs a particularset of flow entries in switch 120B to configure and monitor tunnel 210.These flow entries may include a failure detect flow entry to detectwhen tunnel 210 has potentially failed and a recovery detect flow entryto detect when tunnel 210 has potentially recovered from failure. Forsake of illustration, embodiments will primarily be described withregard to the flow entries programmed switch 120B. However, it should beunderstood that similar flow entries can be programmed in switch 120A toconfigure and monitor tunnel 210. The failure detect flow entry and therecovery detect flow entry are described in further detail herein below.

The failure detect flow entry detects when the tunnel 210 haspotentially failed. In one embodiment, the failure detect flow entryincludes a packet matching criteria that matches packets that arereceived over a tunnel 210 and an instruction to forward matchingpackets to the tunnel processing pipeline (for normal tunnelprocessing). In one embodiment, the SDN controller 110 programs thefailure detect flow entry with a soft timeout such that the failuredetect flow entry times out if no packets match the failure detect flowentry for a specified period of time (e.g., equal to or slightly lessthan the explicit tunnel monitoring interval). In one embodiment, if thefailure detect flow entry times out, the switch 120 removes the failuredetect flow entry and transmits a message to the SDN controller 110indicating that the failure detect flow entry has been removed (thismessage may be referred to herein as a flow removed message).

An example of a failure detect flow entry is shown in Table I.

TABLE I PACKET MATCHING IDLE CRITERIA PRIORITY TIMEOUT INSTRUCTIONSTUNNEL PORT, 50 1 SEC FORWARD LOCAL IP, TO TUNNEL REMOTE IP PROCESSINGPIPELINEThe packet matching criteria of this failure detect flow entry is set tomatch packets received over a specific tunnel 210 (identified by tunnelport, local Internet Protocol (IP) address, and remote IP address). Thepriority of the failure detect flow entry is set to 50. The idle timeoutof the failure detect flow entry is set to 1 second so that the failuredetect flow entry times out if no packets match the failure detect flowentry for 1 second. The instructions of the failure detect flow entryinclude an instruction to forward matching packets to the tunnelprocessing pipeline.

FIG. 3 is a diagram illustrating operations by a switch and an SDNcontroller when a failure detect flow entry times out, according to someembodiments. When tunnel 210 is operational, the packets transmitted byswitch 120A over tunnel 210 will reach switch 120B and match the failuredetect flow entry in switch 120B. As a result, the packets will beforwarded to the tunnel processing pipeline, and be processedaccordingly. However, as shown in FIG. 3, when tunnel 210 fails (e.g.due to a path failure), the packets transmitted by switch 120A overtunnel 210 will not reach switch 120B. In this case, if tunnel 210 doesnot recover within a specified period of time, the failure detect flowentry times out. This results in switch 120B removing the failure detectflow entry and transmitting a flow removed message to SDN controller 110(operation 1). Based on receiving the flow removed message, SDNcontroller 110 may determine that no traffic has been flowing throughtunnel 210 for at least the specified period of time. In response, theSDN controller 110 may enable explicit tunnel monitoring for tunnel 210to determine whether tunnel 210 has failed or if there is just anabsence of traffic flowing through tunnel 210 (operation 2).

It should be noted that when the failure detect flow entry times out, itcan indicate either (1) the tunnel 210 is operational but there is notraffic flowing through the tunnel 210 or (2) the tunnel 210 has failed.When the failure detect flow entry times out, explicit tunnel monitoringcan be used to confirm the reason for flow entry timing out. In the casethat the failure detect flow entry timed out due to no traffic flowingthrough the tunnel 210, explicit tunnel monitoring can be allowed tocontinue until some traffic starts flowing through the tunnel 210.

The recovery detect flow entry detects when the tunnel 210 haspotentially recovered from failure. In one embodiment, the recoverydetect flow entry includes the same packet matching criteria and thesame instructions as the failure detect flow entry. That is, therecovery detect flow entry includes a packet matching criteria thatmatches packets that are received over the tunnel 210 and an instructionto forward matching packets to the tunnel processing pipeline. In oneembodiment, the recovery detect flow entry also includes an instructionreferred to herein as a statistics trigger instruction (e.g.,OFPIT_STAT_TRIGGER instruction in OpenFlow). The statistics triggerinstruction instructs the switch 120 to maintain a statistic associatedwith the recovery detect flow entry and to transmit a message to the SDNcontroller 110 when the statistic associated with the recovery detectflow entry exceeds a threshold value (this message may be referred toherein as a statistics trigger event message). In one embodiment, therecovery detect flow entry includes an indication of the thresholdvalue. For example, the threshold value may be indicated as a number ofpackets, in which case the switch 120 keeps track of the number ofpackets that have matched the recovery detect flow entry (and executedthe statistics trigger instruction of the recovery detect flow entry)and transmits a statistics trigger event message to the SDN controller110 when the number of packets that have matched the recovery detectflow entry exceeds the specified number of packets. As another example,the threshold value may be indicated as a byte count, in which case theswitch 120 keeps track of the cumulative byte count of the packets thathave matched the recovery detect flow entry (and executed the statisticstrigger instruction of the recovery detect flow entry) and transmits astatistics trigger event message to the SDN controller 110 when thecumulative byte count of the packets that have matched the recoverydetect flow entry exceeds the specified byte count. In one embodiment,the statistics trigger instruction includes an indication that thestatistics trigger event message is to be transmitted to the SDNcontroller 110 when the statistic associated with the recovery detectflow entry exceeds any multiple of the threshold value (e.g.,OSPSTF_PERIODIC flag setting in OpenFlow).

In one embodiment, the recovery detect flow entry has a priority that islower than the priority of the corresponding failure detect flow entry.As such, when the switch 120 includes both the failure detect flow entryand the recovery detect flow entry, packets received over the tunnel 210may match the packet matching criteria of both the failure detect flowentry and the recovery detect flow entry, but the switch 120 executesthe instructions of the failure detect flow entry since it has higherpriority. However, after the failure detect flow entry is removed (e.g.,due to the failure detect flow entry timing out), packets received overthe tunnel 210 match the recovery detect flow entry and the switch 120executes the instructions of the recovery detect flow entry (includingthe statistics trigger instruction).

An example of a recovery detect flow entry (corresponding to the failuredetect flow entry shown in Table I) is shown in Table II.

TABLE III PACKET MATCHING IDLE CRITERIA PRIORITY TIMEOUT INSTRUCTIONSTUNNEL PORT, 5 FORWARD TO LOCAL IP, TUNNEL REMOTE IP PROCESSINGPIPELINE; STAT_TRIGGER (THRESHOLDS = 1 PACKET)

The packet matching criteria of the recovery detect flow entry is set tomatch packets received over a specific tunnel 210 (identified by tunnelport, local Internet Protocol (IP) address, and remote IP address). Thispacket matching criteria is typically set to be the same as the packetmatching criteria of the corresponding failure detect flow entry. Thepriority of the recovery detect flow entry is set to 5, which is lowerthan the priority of the corresponding failure detect flow entry (whichwas set to 50). The instructions of the recovery detect flow entryinclude an instruction to forward matching packets to the tunnelprocessing pipeline. In addition, the instructions include a statisticstrigger instruction (STAT_TRIGGER) that instructs the switch 120 totransmit a statistics trigger event message to the SDN controller 110 ifat least one packet matches the recovery detect flow entry (THRESHOLD=1PACKET). In this example, the recovery detect flow entry does not havean idle timeout (it does not time out).

In one embodiment, the statistics trigger instruction uses the followingstructure and fields:

/* Instruction structure for OFPIT_STAT_TRIGGER */ structofp_instruction_stat_trigger {    uint16_t type; /* OFPIT_STAT_TRIGGER*/    uint16_t len; /* Length is padded to 64 bits. */    uint32_tflags; /* Bitmap of OFPSTF_* flags. */    struct ofp_stats thresholds;/* Threshold list. Variable size. */ }; OFP_ASSERT(sizeof(structofp_instruction_stat_trigger) == 16);

The flags field is a bitmap that defines the behavior of the statisticstrigger. It may include a combination of the following flags:

enum ofp_stat_trigger_flags {    OFPSTF_PERIODIC = 1 << 0, /* Triggerfor all multiples    of thresholds. */    OFPSTF_ONLY_FIRST = 1 << 1, /*Trigger on    only first reach threshold. */ };

When the OFPSTF_PERIODIC flag is set, the trigger will apply not only onthe values in the thresholds field, but also on all multiples of thosevalues. It allows, for example, to have a trigger every 100 packets forthe lifetime of the flow. When the OFPSTF_ONLY_FIRST flag is set, onlythe first threshold that is crossed is considered, and other thresholdsare ignored. This allows the SDN controller 110 to receive only a singlestatistics trigger event message for multiple thresholds.

FIG. 4 is a diagram illustrating operations by a switch and an SDNcontroller when a statistic associated with a recovery detect flow entryexceeds a threshold value, according to some embodiments. Continuingwith the example described with reference to FIG. 3, when tunnel 210recovers from failure and traffic starts flowing through tunnel 210again, the packets transmitted by switch 120A over tunnel 210 will reachswitch 120B and match the recovery detect flow entry in switch 120B(since failure detect flow entry has been removed). As a result, thepackets will be forwarded to the tunnel processing pipeline, and beprocessed accordingly. In addition, as shown in FIG. 4, if the statisticassociated with the recovery detect flow entry exceeds the thresholdvalue (or a multiple thereof), switch 120B transmits a statisticstrigger event message to SDN controller 110 (operation 1). Based onreceiving the statistics trigger event message, SDN controller 110 maydetermine that traffic is flowing through tunnel 210 again and that 210tunnel has recovered from failure. In response, SDN controller 110 maydisable explicit tunnel monitoring for tunnel 210 (operation 2) andreprogram the failure detection flow entry in switch 120B (to detectfuture tunnel failures) (operation 3).

In one embodiment, the SDN controller 110 programs a flow entry in theswitch 120 to handle explicit tunnel monitoring packets (e.g., BFDkeep-alive packets). Such a flow entry may be referred to herein as anexplicit tunnel monitoring flow entry. In one embodiment, the explicittunnel monitoring flow entry includes a packet matching criteria thatmatches explicit tunnel monitoring packets that are received over thetunnel 210 and an instruction to forward matching packets to the tunnelmonitoring pipeline (for normal explicit tunnel monitoring processing).In one embodiment, this flow entry has a priority that is higher thanthe priority of the recovery detect flow entry so that the explicittunnel monitoring packets do not trigger a statistics trigger eventmessage (e.g., based on executing the instructions of the recoverydetect flow entry).

An example of an explicit tunnel monitoring flow entry is shown in TableIII.

TABLE IIIII PACKET MATCHING IDLE CRITERIA PRIORITY TIMEOUT INSTRUCTIONSTUNNEL PORT, 10 FORWARD LOCAL IP, TO TUNNEL REMOTE IP, TUN- MONITORINGNEL MONITORING PIPELINE PROTOCOL TYPE

The packet matching criteria of the explicit tunnel monitoring flowentry is set to match packets having an explicit tunnel monitoringprotocol type (e.g., BFD packet) received over a specific tunnel 210(identified by tunnel port, local Internet Protocol (IP) address, andremote IP address). The priority of the explicit tunnel monitoring flowentry is set to 10, which is higher than the priority of thecorresponding recovery detect flow entry (shown in Table II). Theinstructions of the explicit tunnel monitoring flow entry include aninstruction to forward matching packets to the tunnel monitoringpipeline. In this example, the explicit tunnel monitoring flow entrydoes not have an idle timeout (it does not time out).

When explicit tunnel monitoring is enabled for the tunnel 210, theexplicit tunnel monitoring packets (e.g., BFD packets) received over thetunnel 210 may match the packet matching criteria of both the explicittunnel monitoring flow entry and the recovery detect flow entry, but theswitch 120 executes the instructions of the explicit tunnel monitoringflow entry since it has higher priority. This allows the switch 120 tohandle explicit tunnel monitoring packets without triggering astatistics trigger event message.

FIG. 5 is a flow diagram of a process for monitoring a tunnel in an SDNnetwork, according to some embodiments. In one embodiment, the processis performed by a switch 120 in the SDN network 100 (e.g., a networkdevice functioning as a switch 120 in the SDN network 100). Theoperations in this and other flow diagrams will be described withreference to the exemplary embodiments of the other figures. However, itshould be understood that the operations of the flow diagrams can beperformed by embodiments of the invention other than those discussedwith reference to the other figures, and the embodiments of theinvention discussed with reference to these other figures can performoperations different than those discussed with reference to the flowdiagrams.

In one embodiment, the process is initiated by the switch 120 generatinga first flow entry (e.g., failure detect flow entry) (block 510) and asecond flow entry (e.g., recovery detect flow entry) (block 520). Boththe first flow entry and the second flow entry may have a packetmatching criteria that matches packets received over the tunnel 210, butthe second flow entry has a priority that is lower than the priority ofthe first flow entry. As such, if the switch 120 receives a packet thatmatches the packet matching criteria of both flow entries, the switch120 executes the instructions of the first flow entry. In oneembodiment, the first flow entry and the second flow entry are generatedin a foremost flow table of a packet processing pipeline (e.g., table 0in OpenFlow). In one embodiment, the first flow entry and the secondflow entry include an instruction to direct matching packets to a tunnelprocessing pipeline. In one embodiment, the first flow entry times outif no packets match the first flow entry for a given period of time. Inone embodiment, the first flow entry includes an indication of an idletimeout value (e.g., a value indicating how long it takes for the firstflow entry to time out). If the switch 120 determines that the firstflow entry has timed out (decision block 530), the switch 120 removesthe first flow entry (block 540) and transmits a flow removed message tothe SDN controller 110 (block 550) to indicate that the first flow entryhas been removed. This may indicate to the SDN controller 110 that thetunnel 210 has potentially failed and cause the SDN controller 110 toenable explicit tunnel monitoring for the tunnel 210. Returning todecision block 530, if the first flow entry has not timed out, theswitch 120 continues normal packet processing.

Once the first flow entry has been removed, packets received over thetunnel 210 will match the second flow entry. The switch 120 maintains astatistic associated with the second flow entry (e.g., based on astatistics trigger instruction included in the second flow entry) (block555). The switch 120 determines whether the statistic associated withthe second flow entry exceeds a threshold value (decision block decisionblock 560). In one embodiment, the statistic associated with the secondflow entry is a packet count of packets that matched the second flowentry. In another embodiment, the statistic associated with the secondflow entry is a cumulative byte count of packets that matched the secondflow entry. In one embodiment, the second flow entry includes anindication of the threshold value. If the statistic associated with thesecond flow entry has not exceeded the threshold value, the switch 120continues normal packet processing. If the switch 120 determines thatthe statistic associated with the second flow entry has exceeded thethreshold value, the switch 120 transmits a statistics trigger eventmessage to the SDN controller 110 (block 570). This may indicate to theSDN controller 110 that the tunnel 210 has potentially recovered fromfailure and cause the SDN controller 110 to disable explicit tunnelmonitoring for the tunnel 210. In one embodiment, the second flow entryincludes an indication that the statistics trigger event message is tobe transmitted to the SDN controller 110 when the statistic associatedwith the second flow entry exceeds a multiple of the threshold value(e.g., OFPSTF_PERIODIC flag setting in OpenFlow). In this embodiment,the switch 120 transmits a statistics trigger event message to the SDNcontroller 110 whenever the statistic associated with the second flowentry exceeds a multiple of the threshold value (e.g., every packet orevery 10,000 bytes). In one embodiment, after the switch 120 transmitsthe statistics trigger event message to the SDN controller 110, theswitch 120 receives an instruction from the SDN controller 110 toregenerate the first flow entry. The switch 120 may then regenerate thefirst flow entry (block 580) (e.g., according to instructions receivedfrom the SDN controller 110).

In one embodiment, the switch 120 generates a third flow entry (e.g.,explicit tunnel monitoring flow entry) that matches explicit tunnelmonitoring packets (e.g., BFD packets) received over the tunnel 210. Inone embodiment, the third flow entry has a priority that is higher thanthe priority of the second flow entry. This allows the switch 120 tohandle explicit tunnel monitoring packets without triggering astatistics trigger event message.

FIG. 6 is a flow diagram of a process for monitoring a tunnel in an SDNnetwork, according to some embodiments. In one embodiment, the processis performed by an SDN controller 110 in the SDN network 100 (e.g., anetwork device functioning as an SDN controller 110 in the SDN network100).

In one embodiment, the process is initiated by the SDN controller 110transmitting an instruction to a switch 120 to generate a first flowentry that matches packets received over the tunnel 210 (block 610). TheSDN controller 110 also transmits an instruction to the switch 120 togenerate a second flow entry that matches packets received over thetunnel 210, where the second flow entry has a priority that is lowerthan a priority of the first flow entry (block 620). In one embodiment,the first flow entry is a failure detect flow entry and the second flowentry is a corresponding recovery detect flow entry. The SDN controller110 may subsequently receive a flow removed message from the switch 120indicating that the first flow entry has been removed (block 630). Thismay indicate that the tunnel 210 has potentially failed. In response,the SDN controller 110 may enable explicit tunnel monitoring for thetunnel 210 (block 640).

Subsequently, the SDN controller 110 may receive a statistics triggerevent message from the switch 120 indicating that a statistic associatedwith the second flow entry exceeded a threshold value (block 650). Thismay indicate that the tunnel 210 has potentially recovered from failure.In response, the SDN controller 110 may disable explicit tunnelmonitoring for the tunnel 210 (block 660) and transmit an instruction tothe switch 120 to regenerate the first flow entry (block 670).

An advantage of the embodiments disclosed herein is that they onlyresort to explicit tunnel monitoring when there is no traffic flowingthrough the tunnel 210, and thus the bandwidth usage of the tunnel 210and the processing load at the end points of the tunnel 210 (e.g.,switch 120A and switch 120B) can be reduced. This advantage becomes evenmore pronounced as the number of switches 120 in the data planeincreases (since this increases the number of tunnels 210 and thus alsoincreases the number of explicit tunnel monitoring packets needed).Another advantage of the embodiments disclosed herein is that they avoidmuch of the latency that is typically involved with controller-driventunnel monitoring, where the packet path ofcontroller->switch-1->switch-2->controller is latency prone. The pathfrom controller->switch-1 and switch-2->controller contributes to amajor portion of the latency as these paths lie on the control plane ofthe network. Other advantages will be apparent to one having ordinaryskill in the art from the disclosure provided herein.

FIG. 7A illustrates connectivity between network devices (NDs) within anexemplary network, as well as three exemplary implementations of theNDs, according to some embodiments. FIG. 7A shows NDs 700A-H, and theirconnectivity by way of lines between 700A-700B, 700B-700C, 700C-700D,700D-700E, 700E-700F, 700F-700G, and 700A-700G, as well as between 700Hand each of 700A, 700C, 700D, and 700G. These NDs are physical devices,and the connectivity between these NDs can be wireless or wired (oftenreferred to as a link). An additional line extending from NDs 700A,700E, and 700F illustrates that these NDs act as ingress and egresspoints for the network (and thus, these NDs are sometimes referred to asedge NDs; while the other NDs may be called core NDs).

Two of the exemplary ND implementations in FIG. 7A are: 1) aspecial-purpose network device 702 that uses custom application-specificintegrated-circuits (ASICs) and a special-purpose operating system (OS);and 2) a general purpose network device 704 that uses commonoff-the-shelf (COTS) processors and a standard OS.

The special-purpose network device 702 includes networking hardware 710comprising a set of one or more processor(s) 712, forwarding resource(s)714 (which typically include one or more ASICs and/or networkprocessors), and physical network interfaces (NIs) 716 (through whichnetwork connections are made, such as those shown by the connectivitybetween NDs 700A-H), as well as non-transitory machine readable storagemedia 718 having stored therein networking software 720. Duringoperation, the networking software 720 may be executed by the networkinghardware 710 to instantiate a set of one or more networking softwareinstance(s) 722. Each of the networking software instance(s) 722, andthat part of the networking hardware 710 that executes that networksoftware instance (be it hardware dedicated to that networking softwareinstance and/or time slices of hardware temporally shared by thatnetworking software instance with others of the networking softwareinstance(s) 722), form a separate virtual network element 730A-R. Eachof the virtual network element(s) (VNEs) 730A-R includes a controlcommunication and configuration module 732A-R (sometimes referred to asa local control module or control communication module) and forwardingtable(s) 734A-R, such that a given virtual network element (e.g., 730A)includes the control communication and configuration module (e.g.,732A), a set of one or more forwarding table(s) (e.g., 734A), and thatportion of the networking hardware 710 that executes the virtual networkelement (e.g., 730A).

In one embodiment software 720 includes code such as tunnel monitoringcomponent 725, which when executed by networking hardware 710, causesthe special-purpose network device 702 to perform operations of one ormore embodiments of the present invention as part of networking softwareinstances 722.

The special-purpose network device 702 is often physically and/orlogically considered to include: 1) a ND control plane 724 (sometimesreferred to as a control plane) comprising the processor(s) 712 thatexecute the control communication and configuration module(s) 732A-R;and 2) a ND forwarding plane 726 (sometimes referred to as a forwardingplane, a data plane, or a media plane) comprising the forwardingresource(s) 714 that utilize the forwarding table(s) 734A-R and thephysical NIs 716. By way of example, where the ND is a router (or isimplementing routing functionality), the ND control plane 724 (theprocessor(s) 712 executing the control communication and configurationmodule(s) 732A-R) is typically responsible for participating incontrolling how data (e.g., packets) is to be routed (e.g., the next hopfor the data and the outgoing physical NI for that data) and storingthat routing information in the forwarding table(s) 734A-R, and the NDforwarding plane 726 is responsible for receiving that data on thephysical NIs 716 and forwarding that data out the appropriate ones ofthe physical NIs 716 based on the forwarding table(s) 734A-R.

FIG. 7B illustrates an exemplary way to implement the special-purposenetwork device 702 according to some embodiments. FIG. 7B shows aspecial-purpose network device including cards 738 (typically hotpluggable). While in some embodiments the cards 738 are of two types(one or more that operate as the ND forwarding plane 726 (sometimescalled line cards), and one or more that operate to implement the NDcontrol plane 724 (sometimes called control cards)), alternativeembodiments may combine functionality onto a single card and/or includeadditional card types (e.g., one additional type of card is called aservice card, resource card, or multi-application card). A service cardcan provide specialized processing (e.g., Layer 4 to Layer 7 services(e.g., firewall, Internet Protocol Security (IPsec), Secure SocketsLayer (SSL)/Transport Layer Security (TLS), Intrusion Detection System(IDS), peer-to-peer (P2P), Voice over IP (VoIP) Session BorderController, Mobile Wireless Gateways (Gateway General Packet RadioService (GPRS) Support Node (GGSN), Evolved Packet Core (EPC) Gateway)).By way of example, a service card may be used to terminate IPsec tunnelsand execute the attendant authentication and encryption algorithms.These cards are coupled together through one or more interconnectmechanisms illustrated as backplane 736 (e.g., a first full meshcoupling the line cards and a second full mesh coupling all of thecards).

Returning to FIG. 7A, the general purpose network device 704 includeshardware 740 comprising a set of one or more processor(s) 742 (which areoften COTS processors) and physical NIs 746, as well as non-transitorymachine readable storage media 748 having stored therein software 750.During operation, the processor(s) 742 execute the software 750 toinstantiate one or more sets of one or more applications 764A-R. Whileone embodiment does not implement virtualization, alternativeembodiments may use different forms of virtualization. For example, inone such alternative embodiment the virtualization layer 754 representsthe kernel of an operating system (or a shim executing on a baseoperating system) that allows for the creation of multiple instances762A-R called software containers that may each be used to execute one(or more) of the sets of applications 764A-R; where the multiplesoftware containers (also called virtualization engines, virtual privateservers, or jails) are user spaces (typically a virtual memory space)that are separate from each other and separate from the kernel space inwhich the operating system is run; and where the set of applicationsrunning in a given user space, unless explicitly allowed, cannot accessthe memory of the other processes. In another such alternativeembodiment the virtualization layer 754 represents a hypervisor(sometimes referred to as a virtual machine monitor (VMM)) or ahypervisor executing on top of a host operating system, and each of thesets of applications 764A-R is run on top of a guest operating systemwithin an instance 762A-R called a virtual machine (which may in somecases be considered a tightly isolated form of software container) thatis run on top of the hypervisor—the guest operating system andapplication may not know they are running on a virtual machine asopposed to running on a “bare metal” host electronic device, or throughpara-virtualization the operating system and/or application may be awareof the presence of virtualization for optimization purposes. In yetother alternative embodiments, one, some or all of the applications areimplemented as unikernel(s), which can be generated by compilingdirectly with an application only a limited set of libraries (e.g., froma library operating system (LibOS) including drivers/libraries of OSservices) that provide the particular OS services needed by theapplication. As a unikernel can be implemented to run directly onhardware 740, directly on a hypervisor (in which case the unikernel issometimes described as running within a LibOS virtual machine), or in asoftware container, embodiments can be implemented fully with unikernelsrunning directly on a hypervisor represented by virtualization layer754, unikernels running within software containers represented byinstances 762A-R, or as a combination of unikernels and theabove-described techniques (e.g., unikernels and virtual machines bothrun directly on a hypervisor, unikernels and sets of applications thatare run in different software containers).

The instantiation of the one or more sets of one or more applications764A-R, as well as virtualization if implemented, are collectivelyreferred to as software instance(s) 752. Each set of applications764A-R, corresponding virtualization construct (e.g., instance 762A-R)if implemented, and that part of the hardware 740 that executes them (beit hardware dedicated to that execution and/or time slices of hardwaretemporally shared), forms a separate virtual network element(s) 760A-R.

The virtual network element(s) 760A-R perform similar functionality tothe virtual network element(s) 730A-R—e.g., similar to the controlcommunication and configuration module(s) 732A and forwarding table(s)734A (this virtualization of the hardware 740 is sometimes referred toas network function virtualization (NFV)). Thus, NFV may be used toconsolidate many network equipment types onto industry standard highvolume server hardware, physical switches, and physical storage, whichcould be located in Data centers, NDs, and customer premise equipment(CPE). While embodiments of the invention are illustrated with eachinstance 762A-R corresponding to one VNE 760A-R, alternative embodimentsmay implement this correspondence at a finer level granularity (e.g.,line card virtual machines virtualize line cards, control card virtualmachine virtualize control cards, etc.); it should be understood thatthe techniques described herein with reference to a correspondence ofinstances 762A-R to VNEs also apply to embodiments where such a finerlevel of granularity and/or unikernels are used.

In certain embodiments, the virtualization layer 754 includes a virtualswitch that provides similar forwarding services as a physical Ethernetswitch. Specifically, this virtual switch forwards traffic betweeninstances 762A-R and the physical NI(s) 746, as well as optionallybetween the instances 762A-R; in addition, this virtual switch mayenforce network isolation between the VNEs 760A-R that by policy are notpermitted to communicate with each other (e.g., by honoring virtuallocal area networks (VLANs)).

In one embodiment, software 750 includes code such as tunnel monitoringcomponent 763, which when executed by processor(s) 742, cause thegeneral purpose network device 704 to perform operations of one or moreembodiments of the present invention as part of software instances762A-R.

The third exemplary ND implementation in FIG. 7A is a hybrid networkdevice 706, which includes both custom ASICs/special-purpose OS and COTSprocessors/standard OS in a single ND or a single card within an ND. Incertain embodiments of such a hybrid network device, a platform VM(i.e., a VM that that implements the functionality of thespecial-purpose network device 702) could provide forpara-virtualization to the networking hardware present in the hybridnetwork device 706.

Regardless of the above exemplary implementations of an ND, when asingle one of multiple VNEs implemented by an ND is being considered(e.g., only one of the VNEs is part of a given virtual network) or whereonly a single VNE is currently being implemented by an ND, the shortenedterm network element (NE) is sometimes used to refer to that VNE. Alsoin all of the above exemplary implementations, each of the VNEs (e.g.,VNE(s) 730A-R, VNEs 760A-R, and those in the hybrid network device 706)receives data on the physical NIs (e.g., 716, 746) and forwards thatdata out the appropriate ones of the physical NIs (e.g., 716, 746). Forexample, a VNE implementing IP router functionality forwards IP packetson the basis of some of the IP header information in the IP packet;where IP header information includes source IP address, destination IPaddress, source port, destination port (where “source port” and“destination port” refer herein to protocol ports, as opposed tophysical ports of a ND), transport protocol (e.g., user datagramprotocol (UDP), Transmission Control Protocol (TCP), and differentiatedservices code point (DSCP) values.

FIG. 7C illustrates various exemplary ways in which VNEs may be coupledaccording to some embodiments. FIG. 7C shows VNEs 770A.1-770A.P (andoptionally VNEs 770A.Q-770A.R) implemented in ND 700A and VNE 770H.1 inND 700H. In FIG. 7C, VNEs 770A.1-P are separate from each other in thesense that they can receive packets from outside ND 700A and forwardpackets outside of ND 700A; VNE 770A. 1 is coupled with VNE 770H.1, andthus they communicate packets between their respective NDs; VNE770A.2-770A.3 may optionally forward packets between themselves withoutforwarding them outside of the ND 700A; and VNE 770A.P may optionally bethe first in a chain of VNEs that includes VNE 770A.Q followed by VNE770A.R (this is sometimes referred to as dynamic service chaining, whereeach of the VNEs in the series of VNEs provides a differentservice—e.g., one or more layer 4-7 network services). While FIG. 7Cillustrates various exemplary relationships between the VNEs,alternative embodiments may support other relationships (e.g.,more/fewer VNEs, more/fewer dynamic service chains, multiple differentdynamic service chains with some common VNEs and some different VNEs).

The NDs of FIG. 7A, for example, may form part of the Internet or aprivate network; and other electronic devices (not shown; such as enduser devices including workstations, laptops, netbooks, tablets, palmtops, mobile phones, smartphones, phablets, multimedia phones, VoiceOver Internet Protocol (VOIP) phones, terminals, portable media players,GPS units, wearable devices, gaming systems, set-top boxes, Internetenabled household appliances) may be coupled to the network (directly orthrough other networks such as access networks) to communicate over thenetwork (e.g., the Internet or virtual private networks (VPNs) overlaidon (e.g., tunneled through) the Internet) with each other (directly orthrough servers) and/or access content and/or services. Such contentand/or services are typically provided by one or more servers (notshown) belonging to a service/content provider or one or more end userdevices (not shown) participating in a peer-to-peer (P2P) service, andmay include, for example, public webpages (e.g., free content, storefronts, search services), private webpages (e.g., username/passwordaccessed webpages providing email services), and/or corporate networksover VPNs. For instance, end user devices may be coupled (e.g., throughcustomer premise equipment coupled to an access network (wired orwirelessly)) to edge NDs, which are coupled (e.g., through one or morecore NDs) to other edge NDs, which are coupled to electronic devicesacting as servers. However, through compute and storage virtualization,one or more of the electronic devices operating as the NDs in FIG. 7Amay also host one or more such servers (e.g., in the case of the generalpurpose network device 704, one or more of the software instances 762A-Rmay operate as servers; the same would be true for the hybrid networkdevice 706; in the case of the special-purpose network device 702, oneor more such servers could also be run on a virtualization layerexecuted by the processor(s) 712); in which case the servers are said tobe co-located with the VNEs of that ND.

A virtual network is a logical abstraction of a physical network (suchas that in FIG. 7A) that provides network services (e.g., L2 and/or L3services). A virtual network can be implemented as an overlay network(sometimes referred to as a network virtualization overlay) thatprovides network services (e.g., layer 2 (L2, data link layer) and/orlayer 3 (L3, network layer) services) over an underlay network (e.g., anL3 network, such as an Internet Protocol (IP) network that uses tunnels(e.g., generic routing encapsulation (GRE), layer 2 tunneling protocol(L2TP), IPSec) to create the overlay network).

A network virtualization edge (NVE) sits at the edge of the underlaynetwork and participates in implementing the network virtualization; thenetwork-facing side of the NVE uses the underlay network to tunnelframes to and from other NVEs; the outward-facing side of the NVE sendsand receives data to and from systems outside the network. A virtualnetwork instance (VNI) is a specific instance of a virtual network on aNVE (e.g., a NE/VNE on an ND, a part of a NE/VNE on a ND where thatNE/VNE is divided into multiple VNEs through emulation); one or moreVNIs can be instantiated on an NVE (e.g., as different VNEs on an ND). Avirtual access point (VAP) is a logical connection point on the NVE forconnecting external systems to a virtual network; a VAP can be physicalor virtual ports identified through logical interface identifiers (e.g.,a VLAN ID).

Examples of network services include: 1) an Ethernet LAN emulationservice (an Ethernet-based multipoint service similar to an InternetEngineering Task Force (IETF) Multiprotocol Label Switching (MPLS) orEthernet VPN (EVPN) service) in which external systems areinterconnected across the network by a LAN environment over the underlaynetwork (e.g., an NVE provides separate L2 VNIs (virtual switchinginstances) for different such virtual networks, and L3 (e.g., IP/MPLS)tunneling encapsulation across the underlay network); and 2) avirtualized IP forwarding service (similar to IETF IP VPN (e.g., BorderGateway Protocol (BGP)/MPLS IPVPN) from a service definitionperspective) in which external systems are interconnected across thenetwork by an L3 environment over the underlay network (e.g., an NVEprovides separate L3 VNIs (forwarding and routing instances) fordifferent such virtual networks, and L3 (e.g., IP/MPLS) tunnelingencapsulation across the underlay network)). Network services may alsoinclude quality of service capabilities (e.g., traffic classificationmarking, traffic conditioning and scheduling), security capabilities(e.g., filters to protect customer premises from network-originatedattacks, to avoid malformed route announcements), and managementcapabilities (e.g., full detection and processing).

FIG. 7D illustrates a network with a single network element on each ofthe NDs of FIG. 7A, and within this straight forward approach contrastsa traditional distributed approach (commonly used by traditionalrouters) with a centralized approach for maintaining reachability andforwarding information (also called network control), according to someembodiments. Specifically, FIG. 7D illustrates network elements (NEs)770A-H with the same connectivity as the NDs 700A-H of FIG. 7A.

FIG. 7D illustrates that the distributed approach 772 distributesresponsibility for generating the reachability and forwardinginformation across the NEs 770A-H; in other words, the process ofneighbor discovery and topology discovery is distributed.

For example, where the special-purpose network device 702 is used, thecontrol communication and configuration module(s) 732A-R of the NDcontrol plane 724 typically include a reachability and forwardinginformation module to implement one or more routing protocols (e.g., anexterior gateway protocol such as Border Gateway Protocol (BGP),Interior Gateway Protocol(s) (IGP) (e.g., Open Shortest Path First(OSPF), Intermediate System to Intermediate System (IS-IS), RoutingInformation Protocol (RIP), Label Distribution Protocol (LDP), ResourceReservation Protocol (RSVP) (including RSVP-Traffic Engineering (TE):Extensions to RSVP for LSP Tunnels and Generalized Multi-Protocol LabelSwitching (GMPLS) Signaling RSVP-TE)) that communicate with other NEs toexchange routes, and then selects those routes based on one or morerouting metrics. Thus, the NEs 770A-H (e.g., the processor(s) 712executing the control communication and configuration module(s) 732A-R)perform their responsibility for participating in controlling how data(e.g., packets) is to be routed (e.g., the next hop for the data and theoutgoing physical NI for that data) by distributively determining thereachability within the network and calculating their respectiveforwarding information. Routes and adjacencies are stored in one or morerouting structures (e.g., Routing Information Base (RIB), LabelInformation Base (LIB), one or more adjacency structures) on the NDcontrol plane 724. The ND control plane 724 programs the ND forwardingplane 726 with information (e.g., adjacency and route information) basedon the routing structure(s). For example, the ND control plane 724programs the adjacency and route information into one or more forwardingtable(s) 734A-R (e.g., Forwarding Information Base (FIB), LabelForwarding Information Base (LFIB), and one or more adjacencystructures) on the ND forwarding plane 726. For layer 2 forwarding, theND can store one or more bridging tables that are used to forward databased on the layer 2 information in that data. While the above exampleuses the special-purpose network device 702, the same distributedapproach 772 can be implemented on the general purpose network device704 and the hybrid network device 706.

FIG. 7D illustrates that a centralized approach 774 (also known assoftware defined networking (SDN)) that decouples the system that makesdecisions about where traffic is sent from the underlying systems thatforwards traffic to the selected destination. The illustratedcentralized approach 774 has the responsibility for the generation ofreachability and forwarding information in a centralized control plane776 (sometimes referred to as a SDN control module, controller, networkcontroller, OpenFlow controller, SDN controller, control plane node,network virtualization authority, or management control entity), andthus the process of neighbor discovery and topology discovery iscentralized. The centralized control plane 776 has a south boundinterface 782 with a data plane 780 (sometime referred to theinfrastructure layer, network forwarding plane, or forwarding plane(which should not be confused with a ND forwarding plane)) that includesthe NEs 770A-H (sometimes referred to as switches, forwarding elements,data plane elements, or nodes). The centralized control plane 776includes a network controller 778, which includes a centralizedreachability and forwarding information module 779 that determines thereachability within the network and distributes the forwardinginformation to the NEs 770A-H of the data plane 780 over the south boundinterface 782 (which may use the OpenFlow protocol). Thus, the networkintelligence is centralized in the centralized control plane 776executing on electronic devices that are typically separate from theNDs. In one embodiment, the network controller 778 includes a tunnelmonitoring component 781 that when executed by the network controller778, causes the network controller 778 to perform operations of one ormore embodiments of the present invention.

For example, where the special-purpose network device 702 is used in thedata plane 780, each of the control communication and configurationmodule(s) 732A-R of the ND control plane 724 typically include a controlagent that provides the VNE side of the south bound interface 782. Inthis case, the ND control plane 724 (the processor(s) 712 executing thecontrol communication and configuration module(s) 732A-R) performs itsresponsibility for participating in controlling how data (e.g., packets)is to be routed (e.g., the next hop for the data and the outgoingphysical NI for that data) through the control agent communicating withthe centralized control plane 776 to receive the forwarding information(and in some cases, the reachability information) from the centralizedreachability and forwarding information module 779 (it should beunderstood that in some embodiments of the invention, the controlcommunication and configuration module(s) 732A-R, in addition tocommunicating with the centralized control plane 776, may also play somerole in determining reachability and/or calculating forwardinginformation—albeit less so than in the case of a distributed approach;such embodiments are generally considered to fall under the centralizedapproach 774, but may also be considered a hybrid approach).

While the above example uses the special-purpose network device 702, thesame centralized approach 774 can be implemented with the generalpurpose network device 704 (e.g., each of the VNE 760A-R performs itsresponsibility for controlling how data (e.g., packets) is to be routed(e.g., the next hop for the data and the outgoing physical NI for thatdata) by communicating with the centralized control plane 776 to receivethe forwarding information (and in some cases, the reachabilityinformation) from the centralized reachability and forwardinginformation module 779; it should be understood that in some embodimentsof the invention, the VNEs 760A-R, in addition to communicating with thecentralized control plane 776, may also play some role in determiningreachability and/or calculating forwarding information—albeit less sothan in the case of a distributed approach) and the hybrid networkdevice 706. In fact, the use of SDN techniques can enhance the NFVtechniques typically used in the general purpose network device 704 orhybrid network device 706 implementations as NFV is able to support SDNby providing an infrastructure upon which the SDN software can be run,and NFV and SDN both aim to make use of commodity server hardware andphysical switches.

FIG. 7D also shows that the centralized control plane 776 has a northbound interface 784 to an application layer 786, in which residesapplication(s) 788. The centralized control plane 776 has the ability toform virtual networks 792 (sometimes referred to as a logical forwardingplane, network services, or overlay networks (with the NEs 770A-H of thedata plane 780 being the underlay network)) for the application(s) 788.Thus, the centralized control plane 776 maintains a global view of allNDs and configured NEs/VNEs, and it maps the virtual networks to theunderlying NDs efficiently (including maintaining these mappings as thephysical network changes either through hardware (ND, link, or NDcomponent) failure, addition, or removal).

While FIG. 7D shows the distributed approach 772 separate from thecentralized approach 774, the effort of network control may bedistributed differently or the two combined in certain embodiments ofthe invention. For example: 1) embodiments may generally use thecentralized approach (SDN) 774, but have certain functions delegated tothe NEs (e.g., the distributed approach may be used to implement one ormore of fault monitoring, performance monitoring, protection switching,and primitives for neighbor and/or topology discovery); or 2)embodiments of the invention may perform neighbor discovery and topologydiscovery via both the centralized control plane and the distributedprotocols, and the results compared to raise exceptions where they donot agree. Such embodiments are generally considered to fall under thecentralized approach 774, but may also be considered a hybrid approach.

While FIG. 7D illustrates the simple case where each of the NDs 700A-Himplements a single NE 770A-H, it should be understood that the networkcontrol approaches described with reference to FIG. 7D also work fornetworks where one or more of the NDs 700A-H implement multiple VNEs(e.g., VNEs 730A-R, VNEs 760A-R, those in the hybrid network device706). Alternatively or in addition, the network controller 778 may alsoemulate the implementation of multiple VNEs in a single ND.Specifically, instead of (or in addition to) implementing multiple VNEsin a single ND, the network controller 778 may present theimplementation of a VNE/NE in a single ND as multiple VNEs in thevirtual networks 792 (all in the same one of the virtual network(s) 792,each in different ones of the virtual network(s) 792, or somecombination). For example, the network controller 778 may cause an ND toimplement a single VNE (a NE) in the underlay network, and thenlogically divide up the resources of that NE within the centralizedcontrol plane 776 to present different VNEs in the virtual network(s)792 (where these different VNEs in the overlay networks are sharing theresources of the single VNE/NE implementation on the ND in the underlaynetwork).

On the other hand, FIGS. 7E and 7F respectively illustrate exemplaryabstractions of NEs and VNEs that the network controller 778 may presentas part of different ones of the virtual networks 792. FIG. 7Eillustrates the simple case of where each of the NDs 700A-H implements asingle NE 770A-H (see FIG. 7D), but the centralized control plane 776has abstracted multiple of the NEs in different NDs (the NEs 770A-C andG-H) into (to represent) a single NE 7701 in one of the virtualnetwork(s) 792 of FIG. 7D, according to some embodiments. FIG. 7E showsthat in this virtual network, the NE 7701 is coupled to NE 770D and770F, which are both still coupled to NE 770E.

FIG. 7F illustrates a case where multiple VNEs (VNE 770A.1 and VNE770H.1) are implemented on different NDs (ND 700A and ND 700H) and arecoupled to each other, and where the centralized control plane 776 hasabstracted these multiple VNEs such that they appear as a single VNE770T within one of the virtual networks 792 of FIG. 7D, according tosome embodiments. Thus, the abstraction of a NE or VNE can span multipleNDs.

While some embodiments of the invention implement the centralizedcontrol plane 776 as a single entity (e.g., a single instance ofsoftware running on a single electronic device), alternative embodimentsmay spread the functionality across multiple entities for redundancyand/or scalability purposes (e.g., multiple instances of softwarerunning on different electronic devices).

Similar to the network device implementations, the electronic device(s)running the centralized control plane 776, and thus the networkcontroller 778 including the centralized reachability and forwardinginformation module 779, may be implemented a variety of ways (e.g., aspecial purpose device, a general-purpose (e.g., COTS) device, or hybriddevice). These electronic device(s) would similarly includeprocessor(s), a set or one or more physical NIs, and a non-transitorymachine-readable storage medium having stored thereon the centralizedcontrol plane software. For instance, FIG. 8 illustrates, a generalpurpose control plane device 804 including hardware 840 comprising a setof one or more processor(s) 842 (which are often COTS processors) andphysical NIs 846, as well as non-transitory machine readable storagemedia 848 having stored therein centralized control plane (CCP) software850 and a tunnel monitoring component 851.

In embodiments that use compute virtualization, the processor(s) 842typically execute software to instantiate a virtualization layer 854(e.g., in one embodiment the virtualization layer 854 represents thekernel of an operating system (or a shim executing on a base operatingsystem) that allows for the creation of multiple instances 862A-R calledsoftware containers (representing separate user spaces and also calledvirtualization engines, virtual private servers, or jails) that may eachbe used to execute a set of one or more applications; in anotherembodiment the virtualization layer 854 represents a hypervisor(sometimes referred to as a virtual machine monitor (VMM)) or ahypervisor executing on top of a host operating system, and anapplication is run on top of a guest operating system within an instance862A-R called a virtual machine (which in some cases may be considered atightly isolated form of software container) that is run by thehypervisor; in another embodiment, an application is implemented as aunikernel, which can be generated by compiling directly with anapplication only a limited set of libraries (e.g., from a libraryoperating system (LibOS) including drivers/libraries of OS services)that provide the particular OS services needed by the application, andthe unikernel can run directly on hardware 840, directly on a hypervisorrepresented by virtualization layer 854 (in which case the unikernel issometimes described as running within a LibOS virtual machine), or in asoftware container represented by one of instances 862A-R). Again, inembodiments where compute virtualization is used, during operation aninstance of the CCP software 850 (illustrated as CCP instance 876A) isexecuted (e.g., within the instance 862A) on the virtualization layer854. In embodiments where compute virtualization is not used, the CCPinstance 876A is executed, as a unikernel or on top of a host operatingsystem, on the “bare metal” general purpose control plane device 804.The instantiation of the CCP instance 876A, as well as thevirtualization layer 854 and instances 862A-R if implemented, arecollectively referred to as software instance(s) 852.

In some embodiments, the CCP instance 876A includes a network controllerinstance 878. The network controller instance 878 includes a centralizedreachability and forwarding information module instance 879 (which is amiddleware layer providing the context of the network controller 778 tothe operating system and communicating with the various NEs), and an CCPapplication layer 880 (sometimes referred to as an application layer)over the middleware layer (providing the intelligence required forvarious network operations such as protocols, network situationalawareness, and user-interfaces). At a more abstract level, this CCPapplication layer 880 within the centralized control plane 776 workswith virtual network view(s) (logical view(s) of the network) and themiddleware layer provides the conversion from the virtual networks tothe physical view.

The tunnel monitoring component 851 can be executed by hardware 840 toperform operations of one or more embodiments of the present inventionas part of software instances 852.

The centralized control plane 776 transmits relevant messages to thedata plane 780 based on CCP application layer 880 calculations andmiddleware layer mapping for each flow. A flow may be defined as a setof packets whose headers match a given pattern of bits; in this sense,traditional IP forwarding is also flow-based forwarding where the flowsare defined by the destination IP address for example; however, in otherimplementations, the given pattern of bits used for a flow definitionmay include more fields (e.g., 10 or more) in the packet headers.Different NDs/NEs/VNEs of the data plane 780 may receive differentmessages, and thus different forwarding information. The data plane 780processes these messages and programs the appropriate flow informationand corresponding actions in the forwarding tables (sometime referred toas flow tables) of the appropriate NE/VNEs, and then the NEs/VNEs mapincoming packets to flows represented in the forwarding tables andforward packets based on the matches in the forwarding tables.

Standards such as OpenFlow define the protocols used for the messages,as well as a model for processing the packets. The model for processingpackets includes header parsing, packet classification, and makingforwarding decisions. Header parsing describes how to interpret a packetbased upon a well-known set of protocols. Some protocol fields are usedto build a match structure (or key) that will be used in packetclassification (e.g., a first key field could be a source media accesscontrol (MAC) address, and a second key field could be a destination MACaddress).

Packet classification involves executing a lookup in memory to classifythe packet by determining which entry (also referred to as a forwardingtable entry or flow entry) in the forwarding tables best matches thepacket based upon the match structure, or key, of the forwarding tableentries. It is possible that many flows represented in the forwardingtable entries can correspond/match to a packet; in this case the systemis typically configured to determine one forwarding table entry from themany according to a defined scheme (e.g., selecting a first forwardingtable entry that is matched). Forwarding table entries include both aspecific set of match criteria (a set of values or wildcards, or anindication of what portions of a packet should be compared to aparticular value/values/wildcards, as defined by the matchingcapabilities—for specific fields in the packet header, or for some otherpacket content), and a set of one or more actions for the data plane totake on receiving a matching packet. For example, an action may be topush a header onto the packet, for the packet using a particular port,flood the packet, or simply drop the packet. Thus, a forwarding tableentry for IPv4/IPv6 packets with a particular transmission controlprotocol (TCP) destination port could contain an action specifying thatthese packets should be dropped.

Making forwarding decisions and performing actions occurs, based uponthe forwarding table entry identified during packet classification, byexecuting the set of actions identified in the matched forwarding tableentry on the packet.

However, when an unknown packet (for example, a “missed packet” or a“match-miss” as used in OpenFlow parlance) arrives at the data plane780, the packet (or a subset of the packet header and content) istypically forwarded to the centralized control plane 776. Thecentralized control plane 776 will then program forwarding table entriesinto the data plane 780 to accommodate packets belonging to the flow ofthe unknown packet. Once a specific forwarding table entry has beenprogrammed into the data plane 780 by the centralized control plane 776,the next packet with matching credentials will match that forwardingtable entry and take the set of actions associated with that matchedentry.

A network interface (NI) may be physical or virtual; and in the contextof IP, an interface address is an IP address assigned to a NI, be it aphysical NI or virtual NI. A virtual NI may be associated with aphysical NI, with another virtual interface, or stand on its own (e.g.,a loopback interface, a point-to-point protocol interface). A NI(physical or virtual) may be numbered (a NI with an IP address) orunnumbered (a NI without an IP address). A loopback interface (and itsloopback address) is a specific type of virtual NI (and IP address) of aNE/VNE (physical or virtual) often used for management purposes; wheresuch an IP address is referred to as the nodal loopback address. The IPaddress(es) assigned to the NI(s) of a ND are referred to as IPaddresses of that ND; at a more granular level, the IP address(es)assigned to NI(s) assigned to a NE/VNE implemented on a ND can bereferred to as IP addresses of that NE/VNE.

While the flow diagrams in the figures show a particular order ofoperations performed by certain embodiments of the invention, it shouldbe understood that such order is exemplary (e.g., alternativeembodiments may perform the operations in a different order, combinecertain operations, overlap certain operations, etc.).

While the invention has been described in terms of several embodiments,those skilled in the art will recognize that the invention is notlimited to the embodiments described, can be practiced with modificationand alteration within the spirit and scope of the appended claims. Thedescription is thus to be regarded as illustrative instead of limiting.

1. A method implemented by a first switch in a software definednetworking (SDN) network to monitor a tunnel between the first switchand a second switch in the SDN network, the method comprising:generating a first flow entry that matches packets received over thetunnel; generating a second flow entry that matches packet received overthe tunnel, wherein the second flow entry has a priority that is lowerthan a priority of the first flow entry; removing the first flow entryand transmitting a flow removed message to an SDN controller in responseto a determination that the first flow entry has timed out; maintaininga statistic associated with the second flow entry; and transmitting astatistics trigger event message to the SDN controller in response to adetermination that the statistic associated with the second flow entryexceeds a threshold value.
 2. The method of claim 1, whereintransmitting the flow removed message to the SDN controller causes theSDN controller to enable tunnel monitoring for the tunnel.
 3. The methodof claim 2, wherein transmitting the statistics trigger event message tothe SDN controller causes the SDN controller to disable tunnelmonitoring for the tunnel.
 4. The method of claim 1, further comprising:receiving an instruction from the SDN controller to regenerate the firstflow entry after transmitting the statistics trigger event message tothe SDN controller; and regenerating the first flow entry according tothe instruction received from the SDN controller.
 5. The method of claim1, wherein the statistic associated with the second flow entry is apacket count of packets that matched the second flow entry.
 6. Themethod of claim 1, further comprising: generating a third flow entrythat matches explicit tunnel monitoring packets received over thetunnel, wherein the third flow entry has a priority that is higher thanthe priority of the second flow entry.
 7. The method of claim 1, whereinthe first flow entry and the second flow entry include an instruction todirect matching packets to a tunnel processing pipeline.
 8. The methodof claim 1, wherein the first flow entry and the second flow entry aregenerated in a foremost flow table of a packet processing pipeline. 9.The method of claim 1, wherein the first flow entry includes anindication of an idle timeout value.
 10. The method of claim 1, whereinthe second flow entry includes an indication of the threshold value forthe statistic.
 11. The method of claim 10, wherein the second flow entryincludes an indication that the statistics trigger event message is tobe transmitted to the SDN controller when the statistic associated withthe second flow entry exceeds a multiple of the threshold value.
 12. Anetwork device configured to function as a first switch in a softwaredefined networking (SDN) network to monitor a tunnel between the firstswitch and a second switch in the SDN network, the network devicecomprising: a set of one or more processors; and a non-transitorymachine-readable storage medium having stored therein a tunnelmonitoring component, which when executed by the set of one or moreprocessors, causes the network device to generate a first flow entrythat matches packets received over the tunnel, generate a second flowentry that matches packet received over the tunnel, wherein the secondflow entry has a priority that is lower than a priority of the firstflow entry, remove the first flow entry and transmit a flow removedmessage to an SDN controller in response to a determination that thefirst flow entry has timed out, maintain a statistic associated with thesecond flow entry, and transmit a statistics trigger event message tothe SDN controller in response to a determination that the statisticassociated with the second flow entry exceeds a threshold value.
 13. Thenetwork device of claim 12, wherein transmission of the flow removedmessage to the SDN controller is to cause the SDN controller to enabletunnel monitoring for the tunnel.
 14. The network device of claim 13,wherein transmission of the statistics trigger event message to the SDNcontroller is to cause the SDN controller to disable tunnel monitoringfor the tunnel.
 15. The network device of claim 12, wherein the tunnelmonitoring component, when executed by the set of one or moreprocessors, further causes the network device to receive an instructionfrom the SDN controller to regenerate the first flow entry aftertransmitting the statistics trigger event message to the SDN controllerand regenerate the first flow entry according to the instructionreceived from the SDN controller.
 16. The network device of claim 12,wherein the statistic associated with the second flow entry is a packetcount of packets that matched the second flow entry.
 17. Anon-transitory machine-readable medium having computer code storedtherein, which when executed by a set of one or more processors of anetwork device functioning as a first switch in a software definednetworking (SDN) network, causes the network device to performoperations for monitoring a tunnel between the first switch and a secondswitch in the SDN network, the operations comprising: generating a firstflow entry that matches packets received over the tunnel; generating asecond flow entry that matches packet received over the tunnel, whereinthe second flow entry has a priority that is lower than a priority ofthe first flow entry; removing the first flow entry and transmitting aflow removed message to an SDN controller in response to a determinationthat the first flow entry has timed out; maintaining a statisticassociated with the second flow entry; and transmitting a statisticstrigger event message to the SDN controller in response to adetermination that a statistic associated with the second flow entryexceeds a threshold value.
 18. The non-transitory machine-readablemedium of claim 17, wherein the computer code, when executed by the setof one or more processors of the network device, causes the networkdevice to perform further operations comprising: receiving aninstruction from the SDN controller to regenerate the first flow entryafter transmitting the statistics trigger event message to the SDNcontroller; and regenerating the first flow entry according to theinstruction received from the SDN controller.
 19. The non-transitorymachine-readable medium of claim 17, wherein the statistic associatedwith the second flow entry is a packet count of packets that matched thesecond flow entry.
 20. The non-transitory machine-readable medium ofclaim 17, wherein the computer code, when executed by the set of one ormore processors of the network device, causes the network device toperform further operations comprising: generating a third flow entrythat matches explicit tunnel monitoring packets received over thetunnel, wherein the third flow entry has a priority that is higher thanthe priority of the second flow entry.